1. Field of the invention
The present invention relates to a method and a device for designing a photonic network enabling communication of a large amount of information at high speed and low cost.
2. Description of the related art
A technique for allowing various multimedia services to be available regardless of time and location is required. As one of such techniques, there exists a photonic network technique enabling the communication of a large amount of information at high speed and low cost. Among photonic network techniques, a WDM (Wavelength Division Multiplexing) technique of multiplexing a plurality of optical signals having different wavelengths for the communication through a single optical fiber and a photonic node technique of constituting a network regarding each wavelength as a single communication path have been developed. With this development, the realization of a communication network system (hereinafter, referred to as a communication network) which minimizes the cost for introducing equipment (equipment cost) while maintaining high reliability for the reachability of signals is required.
A communication network is constituted by using a linear repeater (1R), a regenerative repeater (3R) and a branch device (HUB). Each of the devices is located in a predetermined station.
The linear repeater amplifies a signal received by itself at a predetermined gain so as to compensate for the attenuation of the signal. In the linear repeater, noise mixed in a main signal is sometimes amplified by signal amplification along with the main signal. Therefore, it sometimes happens in the linear repeater that a signal-to-noise ratio (an SN ratio) is degraded so as not to be reproducible on the receiver side.
The regenerative repeater includes a regenerator. The regenerative repeater first divides a multiplexed signal received by itself for each of channels. Next, the regenerative repeater performs optical-to-electric conversion by the regenerator for each channel so as to perform signal regeneration, regenerated signal amplification and electric-to-optical conversion. Since the signal regeneration is conducted in the regenerative repeater, the degradation of a signal-to-noise ratio can be prevented. The regenerative repeater is more expensive than the linear repeater. Therefore, the equipment cost can be reduced by reducing the number of linear repeaters in network design.
The HUB converts a signal received in a station demanding traffic into a client signal. The HUB branches a path into an appropriate route. The HUB sometimes includes a regenerator for each channel. The HUB executes signal regeneration and regenerated signal amplification by the regenerator as needed. Since paths, each having different starting point and terminal point, intersect and pass in a complex manner in the HUB, each channel is not necessarily required to include a regenerator. Therefore, the equipment cost can be reduced by reducing the number of regenerators provided for each channel.
In non-patent document 1, a conventional design method of a communication network is described. In the above-cited non-patent document, HUBs are first installed in all stations demanding traffic. The HUB includes regenerators for all the channels so as to execute signal regeneration and regenerated signal amplification. Then, only a loss in intensity of a multiplexed signal is examined. Based on the results of examination, a linear repeater and a regenerative repeater are provided between the stations. Then, in a network, in which the reachability of a signal between all the stations is ensured in the above-described manner, path routing with the shortest distance is executed. In the above-cited non-patent document, network resources such as a band or a wavelength are attempted to be efficiently used with the above-described method.
FIGS. 18 and 19 are flowcharts of network designing (referred to as a “basic technique”) described in Japanese Patent Application No. 2002-204461 (unpublished) by the applicant of the present invention. Next, a method of designing a communication network based on the contents of the basic technique will be described. In this realization method, the optimal arrangement (disposition) of a regenerative repeater in consideration of signal noise between certain linear terminal stations is performed.
The terms used in the following description will be defined. A temporary linear repeater and a temporary regenerative repeater denote a linear repeater and a regenerative repeater, which are supposed to be temporarily provided so as to calculate a cumulative signal to noise ratio, respectively. The cumulative signal to noise ratio is a total amount of a signal to noise ratio (including a normalized noise quantity) over a certain 3R section (a regenerative repeater section) or a temporary 3R section (a temporary regenerative repeater section). The temporary 3R section (interval) denotes a section between the temporary regenerative repeater and the terminal station or a section between the temporary regenerative repeater and the regenerative repeater.
First, a total signal to noise ratio in the communication network is calculated (PS01). The total signal to noise ratio corresponds to a total amount of signal to noise ratios between a terminal station and a node adjacent to each other and between the nodes.
Next, the number of regenerative repeaters required for the communication between the terminal stations is calculated (PS02). The number of regenerative repeaters required between the terminal stations is calculated by Equation 1.(Number of regenerative repeaters required between terminal stations)=(Total signal to noise ratio)/(Determination value of the noise quantity transmittable without a regenerative repeater) Number truncated after the decimal point  [Equation 1]
Next, a determination value of the noise quantity over each 3R interval is calculated (PS03). Each temporary 3R section is designed at the following step so that a cumulative signal to noise ratio over this section does not exceed the determination value of the noise quantity calculated at PS03. The determination value of the noise quantity over each 3R section in the communication network is calculated by Equation 2.(Determination value of the noise quantity over each 3R section)=(Total signal to noise ratio)/(Number of regenerative repeaters required between terminal stations)+1  [Equation 2]
Next, for the case where a temporary regenerative repeater is located at the position of each node sequentially from one terminal station P1 to the other terminal station P2, a cumulative signal to noise ratio over a temporary 3R section including the node is calculated (PS04).
Next, it is determined whether the value of the cumulative signal to noise ratio calculated at PS04 exceeds the noise quantity determination value calculated at PS03 or not (PS05). If the cumulative signal to noise ratio does not exceed the noise quantity determination value (PS05-YES), it is determined that a previous node, that is, a node at which the temporary regenerative repeater was provided immediately before a node (current node) at which the temporary regenerative repeater is currently provided is the temporary linear repeater, the terminal station on the transmitter side, or the regenerative repeater. Then, the assignment of the linear repeaters based on the results of determination is carried out (PS06). In the assignment of the linear repeaters, if the previous node is the temporary linear repeater, it is determined that the previous node is the linear repeater. On the other hand, if the previous node is the terminal station on the transmitter side or the regenerative repeater, the process transits to the next process without performing any process.
After the process at PS06, it is determined if the current node is the terminal station on the receiver side (PS07). If the current node is the terminal station on the receiver side (PS07-YES) the process of the system design is terminated (PS08).
On the other hand, if the current node is not a terminal station on the receiver side (PS07-NO), the current node is replaced not by the temporary regenerative repeater but by the temporary linear repeater, and a node to be processed is transited to a next node (PS09). Then, the process for this node is carried out. Specifically, the process after PS04 is carried out in the case where the temporary regenerative repeater is provided at the next node.
If the signal to noise radio exceeds the noise quantity determination value at PS05 (PS05-NO), it is determined whether the previous node is the temporary linear repeater or not (PS10). If the previous node is not the temporary linear repeater (PS10-NO) it is determined that the communication is impossible in the network to be designed (PS11). On the other hand, if the previous node is the temporary linear repeater (PS10-YES), the previous node is determined not as the temporary linear repeater but as the regenerative repeater. Then, the process after PS04 is carried out without transiting the node to be processed to the next node (PS12: the assignment of the regenerative repeaters).
FIG. 20 shows an example of the arrangement (disposition) of devices between terminal stations in a communication network designed based on the basic technique. In the communication network shown in FIG. 20, eleven nodes P2 to P12 are provided between a terminal station P1 and a terminal station P2. Hereinafter, the state where linear repeaters and regenerative repeaters are arranged based on the basic technique in the communication network shown in FIG. 20 will be descried.
First, a total signal to noise ratio is calculated as: 0.20×12=2.40 (PS01). Next, the number of regenerative repeaters required between the terminal stations P1 and P13 is calculated to be “2” by Equation 1 (PS02). Herein, it is supposed that a noise quantity determination value communicable without any regenerative repeaters is “1.00”. Next, a noise quantity determination value over each 3R section is calculated to be “0.80” by Equation 2 (PS03).
Next, the process after PS04 is carried out from the node P2 to the node P12. As a result, the regenerative repeaters are provided at the nodes P5 and P9, whereas the linear repeaters are provided at the remaining nodes, respectively. Therefore, all the cumulative signal to noise ratios over the 3R sections are equalized to be 0.80.
[Non-Patent Document 1]
“Design of ring and mesh based WDM transport networks” by P. Arijs, B. Van Caenegem, P. Demeester, P. Lagasse, W. Van Parys and P. Achten, Optical Networks Magazine, Vol. 1, no. 3, pp. 25 to 40, July 2000
According to the designing method described in the above-cited non-patent document 1, the regenerative repeater is necessarily provided for each station. Therefore, although the reliability of signal performance is high, a communication network, which is redundant and poorly efficient, is designed in view of equipment cost. In order to obtain an economical communication network by reducing the number of regenerative repeaters or regenerators, detailed designing in consideration not only of a loss in intensity of a multiplexed signal but also of noise or dispersion is required. However, if equipment is arranged at the minimum cost in the entire network, the number of combinations of arrangement of devices in the respective stations becomes enormous, considerably increasing the number of steps required for designing. Therefore, it is not practical.
On the other hand, according to the designing method based on the basic technique, signal performance is strictly examined for designing. In the designing method described in the basic technique, however, the signal performance is ensured exclusively for a linear section between terminal stations. In the actual communication network, paths, which respectively have different starting points and terminal points, intersect in a complex manner, and the signal regeneration is carried out for each channel. Therefore, even if a linear repeater, a regenerative repeater, a regenerator in a HUB and the like are efficiently arranged in a linear section, a redundant regenerative repeater or regenerator in the HUB is generated when the overall communication network is considered. In particular, in the HUB at the junction point in a mesh type communication network, there is a possibility that a redundant regenerator is provided.